Toxicity rank of database chemicals

This study of organic and inorganic emissions reveals a pattern of particular importance for the development of a sustainable development policy for the Siberian region. While total volume of pollutants certainly concerns policy makers, of more importance will be to establish which pollutants correlate with the most environmental disturbance or damage. While it is useful to compare total volumes of chemical compounds emitted by given industries, knowing the toxic potential of the various compounds adds depth to the discussion of where emissions must be lowered, and what the potential risks for various endpoints may be.

Given the quality of the data which reports only volume quantities of emitted compounds, creating a risk ranking to determine which chemicals pose the greatest risk in Siberia becomes methodologically difficult. With more information from Russia, it would be feasible to follow the pattern set by the EPA in developing media-specific benchmark values for those chemicals commonly found in surface water, sediment and soil samples at sites (values for soil are still under development). The values are referred to as Ecotox Thresholds (ETs), and are defined as media-specific contaminant concentrations above which there is sufficient concern regarding adverse ecological effects to warrant further site investigation. ETs are designed to provide Superfund site managers with a tool to efficiently identify contaminants that may pose a threat to ecological receptors and focus further site activities on those contaminants and the media in which they are found.² In the future, a methodology such as that for calculating ETs could prove helpful in assessing risk from pollutants in Siberia.

Until such information becomes available, the author has employed the following methodology as an example of what could be used to estimate emissions risk in Siberia. The approach, which uses human health as an endpoint for determining the toxicity rank of the chemicals provided in the IIASA’s Air Pollution database, does not accurately represent the threat to Siberian environments. Comparatively more

2 Such an approach is most useful for screening a particular site, rather than for setting regulatory criteria, site-specific cleanup standards, or abatement goals. The approach may set thresholds too high at some sites for chemicals with the potential to bioaccumulate to toxic levels in upper trophic wildlife (e.g., methyl mercury, PCBs, DDT, dioxins, and lead).

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data exists for the analysis of toxic impact upon humans than for any other environmental endpoint, yet the analysis does move towards the general goal of assessing environmental impact. The report illustrates which chemicals appear to play the most important role in air pollution in Siberia and points to future areas of study for the region. As for the impact upon humans from exposure to harmful compounds, given low population densities in Siberia, exposure risk for humans to this set of atmospheric emissions appears relatively low for individuals living outside of industrial centers. Exposure risk for plants and animals, however, could be more significant. More detailed information about populations, exposure pathways, toxic impacts upon different environmental endpoints, and a variety of other chemical data is needed to carry out detailed impact assessments from air pollution in Siberia.

Using the volume of emissions by site for each compound, the author combined reference dose information for each identified compound with the volume of emissions by site for each compound. A reference dose (RfD) is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Multiplying RfDs for each chemical by total volume of each chemical emitted yields an estimate of the risk value for human health for each pollutant. Chart 2.1 illustrates the compounds which, following this method, appear to have a highly toxic impact upon humans at a given dosage (the RfD).

Risk ranking in this way allows one to divide Siberian emissions into high, medium, and low risk groups.

Knowing which chemicals pose greatest threats to human health (and by way of proxy to forest health), policy makers can more cost-effectively focus on specific abatement goals. For example, the most toxic compound which appears in this analysis is tetraethyl lead, which not only appears consistently throughout the region, but also has some of the most dangerous health impacts for humans. The use of leaded fuels and lack of lead regulation in industrial processes could be responsible for high levels of lead in atmospheric emissions.³ Other toxins that fall into this “high risk” category include mercury, cresol, arsenic, and carbon tetrachloride. Many chemicals fall into the “medium risk” category, including V2O5, toluene, styrene, phenol, naphtalene, manganese, hydrogen sulfide, hydrocyanic acid, hexavalent chromium, hexane, furfural, formaldehyde, carbon disulfide, acrolein, and acetone. In the “lower risk” category fall compounds such as xylene, pyridine, phthalic anhydride, nickel, methanol, hexahydro 2H-azepin-2-one, ethylbenzene, ethyl ether, ethyle acetate, chlorine, and acrylic acid. While these rankings are limited to human health, they do illustrate which chemicals pose greater threats when introducing a dose indicator such as the RfD.

3 The author acknowledges that risk ranking may not be appropriate for chemicals such as lead and mercury. Current research indicates that exposure to such heavy metals may prove toxic at any level.

Chart 2.1 RfD Ranked toxins based upon emissions in Siberia, 1992/93

The present risk-ranking methodology uses human dosage to assign toxic risk to the Siberian pollution database. Future research in the effect of emissions upon specific endpoints such as boreal forests, soil organisms, and animal life will give more insight to the present analysis. Because large areas of Siberia are covered primarily by coniferous and deciduous forests, such measurements would prove more appropriate to measure negative effects of atmospheric emissions. The present study indicates which areas have a higher probability for risk from excessive exposure to high-risk toxins, and what the potential and observed effects upon forest ecosystems are for Siberia and its subregions.

1 10 100 1000 10000 100000 100000

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1E+07 1E+08 1E+09 1E+10 1E+11 1E+12 1E+13 1E Acetone

Acrylic acid Carbon disulfide Chlorine Ethyl acetate Ethylbenzene Furfural Hexane Hydrocyanic acid Manganese Methanol Nickel Phthalic anhydride Styrene Toluene Xylenes

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